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Imaging Chemistry and Biology (pre-2019)

How do medical imaging radioisotopes used for diagnostic imaging and cell tracking affect cancer and immune cells?

Project ID: 2018_206

Student: Ines Costa

1st supervisor: Samantha Terry, King’s College London
2nd supervisor: Gilbert Fruhwirth, King’s College London

Aim of the PhD Project:

Molecular imaging with radionuclides can pinpoint disease locations and measure changes in metabolism and gene expression. Also, reporter gene imaging has long been used to monitor cellular processes but has only recently been used with radionuclides for non-invasive, whole body imaging of cancer or immune cells. This project will determine the sensitivity of cancer cells as well as immune cells to various radionuclides that are used in traditional targeted imaging techniques as well as in reporter gene imaging. The main goals are (i) to pinpoint which radiobiological effects different radioisotopes exert on these cells in the short and long term, and (ii) which cellular doses can be applied without safety concerns.

Project description / background: 

PET and SPECT are radionuclide imaging modalities playing crucial parts in precision medicine as they aid the diagnosis of disease in patients and allow monitoring of therapy response.

Radionuclide reporter gene imaging (RGI) has allowed long-term monitoring of cells in vivo and, recently, emerged as a tool in cell therapy development. It relies on genetic engineering followed by repeated imaging with short-lived radioisotopes (e.g. F-18, Tc -99m, Ga-68) and allows flexible choice of imaging intervals, in stark contrast to direct ex vivo radiolabelling. The main advantages of RGI are: (i) a reduced overall received dose; (ii) better reflection of cell viability; (iii) certainty that label presence remains in the cells of interest; and (iv) theoretically unlimited observation periods. The main drawback is the need for genetic engineering of the cells; however, this is overcome in some cell therapy settings (e.g. CAR-T therapy). Preclinically, RGI has long been established exploiting various imaging modalities to track tumour progression/metastasis, quantify treatment efficacy, or investigate immune cell behaviour. Direct cell labelling has long been employed to track immune cell populations in the clinic, initially using, In-111-oxine, and more recently Zr89-oxine.

However, biological effects of the radionuclides used in these approaches remain poorly understood.  Several radionuclides used for imaging show complex decay patterns, with some releasing Auger electrons that generate complex DNA damage. Others generate high-energy gamma radiation, which has been linked to altered cellular functions and decreased long-term viability. Different cell types (e.g. cancer, normal epithelial or immune cells) are able to switch on repair under different conditions (e.g. normoxic versus hypoxic), significantly complicating matters. The precise effects of imaging radioisotopes used for diagnosis and cell tracking on different cells remains unknown.

This project will determine the effects F-18, Tc-99m, I-123, I-124, I-125, Ga-68, In-111, and Zr-89 have on cancer cells (i.e. proliferation, DNA/chromosomal integrity and repair, treatment resistance) and immune cells (i.e. function, proliferation, plasticity, DNA/chromosomal integrity and repair, migration in vivo). This may influence how imaging tracers such as 18F-FDG (Alliance Medical and Siemens Healthcare), 99mTc-HPMAO (Ceretec; GE Healthcare), 111In-oxine (Oxyquinoline; GE Healthcare) are used as well as informing on the potential therapeutic use of such radionuclides. External beam irradiation and I-131 will be investigated as therapeutic controls. Ga-67 will be used, as it has in the past allowed imaging of infection and inflammation but also Auger electrons.

Preliminary Work:
We will employ existing reporter gene technology based on the non-immunogenic sodium iodide symporter, which has previously been used to establish a variety of traceable cancer and immune cell type.

In-111 when administered to cells as oxine has previously been shown to induce cell toxicity (Figure 1).

Figure 1. Example of clonogenic assay showing clonogenicity (i.e.g ability to proliferate and create clones) is hampered in tumour cells when incubated with 111 Inoxine

Radiobiological studies include determining chromosomal and DNA damage (Figure 2). We will further assess the capacity to sustain proliferation (upon stimulation of certain immune cell types, such as T-cells), function (e.g. tumour cell killing in the case of cytolytic T-cells), migratory potential (for metastatic cancer cells as well as immune cells), and response to latest-generation treatments (for breast cancer cells and melanoma; chemotherapeutics/molecular immunotherapeutics).

Figure 2. Examples of micronucleus in binucleate cancer cells (picture A), comet assay (picture B), chromatid breaks (picture C) and yH2AX (picture D) in irradiated cancer cells.

Left picture: Gammadelta-T cells radio labelled with 89ZR-oxine (400 kBq per million cells) showing DNA damage. Picture on the right: NIS-RFP reporter gene imaging allows accurate longitudinal metastasis tracking (confirmed by ex vivo analysis)

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